Magnesium base alloy



Patented Mar. 16, 1943 MAGNESIUM BASE ALLOY Carl E. Topping, Jackson, Mich., assignor to The Dow- Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application March 23, 1942, Serial No. 435,780

3 Claims.

The invention relates to. a magnesium base alloy particularly suitable for use in manufacture of articles which are required to withstand elevated temperatures while retaining to a large degree their strength properties and resistance to plastic deformation.

Magnesium base alloys are now quite widely used in the various structural arts where a light weight metal is highly desirable, such as in the manufacture of castings, forgings, and the like. However, their use in structural forms which are subjected to elevated temperatures, such as pistons .in internal combustion engines, has not developed to any-marked degree due to the fact that magnesium alloys in general rapidly lose their strength properties and ability to withstand plastic deformation at elevated temperatures to the extent that they are entirely unsuitable for a such use. For use as pistons in automobile and aircraft engines wherein light weight is highly desirable it is necessary that the pistons be able to operate under elevated temperatures of from about 400 to 600 F. without marked plastic deformation, if the piston is to give satisfactory service. At the same time it is necessary that the alloy retain in a large measure its yield strength and tensile strength if it is to be suitable for such use. Additionally, it is desirable that the alloy possess a high thermal conductivity value in order that the heat developed by combustion be rapidly conducted away, thus keeping the operating temperature as low as possible.

It is, therefore,'the principal object of this invention to provide an improved magnesium base 0.05 to 0.2 per cent of calcium possesses the aforementioned desirable properties. The term magnesium used herein and in the appended claims is intended to include magnesium containing the impurities ordinarily-found in the commercially pure metal, such as traces of iron, silicon, and nickel.

Although the new alloy retains satisfactory strength characteristics and resistance to plastic deformation at elevated temperatures throughout the composition range noted above, a preferred I composition range possessing the most satisfactory combination of the properties, strength, resistance to plastic deformation, and high thermal conductivity, is one in which the aluminum is present in an amount of from 1 to 2 per cent, the cadmium in an amount from 2 to 3 per cent, the copper in amount of from about 4 to 8 per cent, manganese in amount of from 0.1 to 0.4 per cent, and the calcium from 0.07 to 0.15 per cent. A specific composition preferred for its excellent combination of properties is one containing 2 per cent of aluminum, 2 per cent cadmium, 4 per cent copper, 0.2 per cent manganese, and 0.1 per cent of calcium.

The following table lists some of the properties of the new alloy at different temperatures and compares'them with the properties .of a related alloy heretofore considered as having desirable propertie in connection with use at elevated temperatures. Examination of the properties listed in the table shows the improvement of the new alloy over that of the closely related alloy at all temperatures tested.

Table Per cent composition magnesium-remainder Tem- Permancnt mold Die cast Yield Tensile Yield Tensile A1 C8 Cd Mn strength strength strength strength F. Lba/aq. in. Lba/sq. in. Lbaleq. in. Lbalsq. in 2.0 2.0 4.0 0.2 70 11,500 000. 17,200 27,600 2.0 0.1 2.0 4.0 0.2 70 15,200 26,800 -19,400 26,100 2.0 2.0 4.0 0.2 000 5,000 8,300 5,400 7,700 2.0 0.1 2.0 4.0 0.2 600 6,500 10,500 6,700

alloy which is adapted for use in the manufacture forms possessing the necessary strength, resistance to plastic deformation, and high thermal conductivity at elevated temperatures.

The invention resides in the discovery that an alloycomposed of from about 1- to 4 per cent of aluminum, from about 1 to 4 'per cent of cadmium, from about 3 to 12 per cent of copper, from about 0.1 to 0.5 per cent of manganese, and from ab A comparison of the properties listed in the above table shows that the new alloy possesses highly superior yield and tensile strengths at elevated temperatures over the similar properties of the related alloy which has heretofore been considered a superior high temperature piston alloy. It will be noted that the yield strength and the tensile strength at elevated temperaout tures in both the permanent mold and the die cast state are highly superior to similar strength properties of the related alloy similarly treated. Additionally it will be noted that the yield strength at ordinary temperatures is markedly superior to similar properties of the related al- 5 loy. The higher strength values of the new alloy at elevated temperatures in comparison with related alloys renders it more suitable for use as pistons in the modern internal combustion engine wherein the trend is toward increasingly higher 1 compression ratios which has'the effect of increasing the temperature of the piston operation and thus further lowering the strength properties.

While the new alloy is most useful in making structural shapes which are to be subjected to 1 operation at elevated temperatures, it may also be suitably used in making forgings, extruded forms and the like.

The new alloy may be prepared by any of the methods usually employed for melting and alloying metals with magnesium, such as by adding the respective metals singly or Jointly to a bath of molten magnesium which is preferably protected from oxidation by a suitable flux. The flux should be substantially free from magnesium chloride if the highest alloying efficiency of the calcium is to be obtained.

I claim:

1. A magnesium base alloy containing from about 1 to 2 per cent of aluminum, from about 2 to 3 per cent of cadmium, from about 4 to 8 per cent of copper, from about 0.1 to 0.4 per cent of manganese, and 0.1 per cent of calcium, the

balance being magnesium.

2. A magnesium base alloy containing from about 1 to 4 per cent of aluminum, from about 1 to 4 per cent of cadmium, from about 3 to 12 per cent of copper, from about 0.1 to 0.5 per cent of manganese, and from about 0.05 to 0.2 per cent of calcium, said alloy being characterized by higher yield and tensile strengths at elevated temperatures as compared to a similar alloy devoid of calcium.

3. A magnesium base alloy containing 2 per cent of aluminum, 2 per cent of cadmium, 4 per cent of copper, 0.2 per cent of manganese, and 0.1 per cent of calcium, the balance being magnesium.

CARL E. TOPPING. 

